1. Field of the Invention
The present invention relates to a depth measuring technique and, more particularly, to a method and apparatus for measuring depth by a stereo method.
2. Description of the Related Art
As shown in “Robot Vision” (Taniuchida, Shokodo 1990, pp. 181–185), a technique is known which detects corresponding points in two images and measures depth of each point in the images by applying the principle of triangulation.
Methods for detecting corresponding points in images are classified roughly into the “feature-based” method and the “region-based” method. The feature-based method establishes correspondence between characteristic parts in images. More specifically, points in a second image that are candidates of correspondence with a point of interest in a first image are identified in successive steps with increasing degree of specificity, based on an attribute of the point of interest in the first image. When a single point is identified, the point is identified as a corresponding point. The region-based method establishes correspondence based on a correlation score of a region surrounding a target pixel. A point with the best correlation score in a search range is determined as a corresponding point.
Accuracy of identifying a corresponding point in the feature-based method depends on accuracy of feature detection. Generally, feature detection tends to pick up noise components as a result of, for example, detecting high frequency components. Accordingly, noise-free detection of a feature is difficult. Moreover, the number of reliable feature points is limited so that depth measurement in the whole image is subject to constraints.
The region-based method is weak in processing an image with repeated patterns. Moreover, if a search range is large, the computation load is correspondingly heavy. If a search range is narrowed, there is likelihood that a corresponding point is missed. As described above, both methods have good points and bad points.
Related Art List
Robot Vision, Taniuchida, Shokodo 1990, pp. 181–185